1. Field of the Invention
This invention relates to new methods and means for remotely determining the range from a datum location to a surface and/or the profile of the surface. More particularly, it concerns methods and devices that enable the position, i.e., range and orientation, of submarine surfaces relative to a moveable object, e.g., a camera, to be determined and/or to remotely ascertain the apparent profile of such surface from the moveable object.
2. Description of the Prior Art
There are many situations in which the location of an object relative to (a) its distance to a surface and/or (b) its orientation to such surface must be determined in order to (1) accurately position the object relative to the surface, (2) to project something from the object to the surface and (3) for many other reasons (see U.S. Pat. No. 4,707,094). This invention is specifically directed to methods and devices useful in those particular situations in which an object, e.g., a camera, a recording system, an imaging device, analysis instrument, etc., must be accurately positioned relative to a surface under conditions that present acute problems in determining the distance and orientation of the object relative to the surface and/or the profile of the surface, particularly in submarine locations. However, it is contemplated that these methods and devices will be put to other uses than in submarine environments.
By way of example of problems associated with submarine operations, as contrasted to terrestrial operations, are those encountered with underwater visual recordings made with photographic or video cameras which typically have limited remote controls. This is particularly true of deep-sea camera systems where camera lens opening and focus are preset and the photographer must somehow arrange for the subject to be at the correct distance, within the field of view and properly oriented with respect to the viewing system at the time of exposure.
Another example occurs in taking an accurate census of living benthonic objects per unit area of a contoured benthonic surface, e.g., in trying to determine what environmental impact a foreign structure, such as a drilling rig, has on the area's living object population over a period of time. Thus, while it is possible to count or record the number of objects within a prescribed submarine field of view, an accurate count per unit benthonic area thereof is not possible unless the profile of the surface is known so the area of surface encompassed by such field can be determined.
Devices and techniques for terrestrial operation of cameras, measurement instruments, etc. are not directly transferable to submarine systems. Differences between the physical properties of air and water result in major differences in the propagation of light and sound in the two media. Additionally, spurious material and signals can cause many "false" exposures or measurements to occur with submarine operations while this is not a serious consideration in use of surface devices. Hence, a system which depends on the propagation of energy waves for operation must be designed for the medium in which it is to be used.
In the case of terrestrial operations, many vision techniques for use with robots, etc. that have been described in the literature are intended to provide or enhance visual capabilities to determine object range, orientation and surface characteristics, e.g., shape, color, texture, etc., see. U.S. Pat. No. 4,459,027; J. Jalkio etal., "Optical Engineering" 24(6), 966-974 (Nov./Dec. 1985) and Livnat etal.--"Optical Engineering" 24(1), 150-152 (Jan./Feb. 1985). Such techniques are usually categorized according to whether triangulation or non-triangulation concepts are employed and whether the system is active or passive. The methods and systems of this invention can be considered to be a passive triangulation type, but are distinguished from schemes found in the prior art which primarily utilize projections of one-dimensional lines, because the systems of this invention involve projections of two-dimensional arrays of spaced dots.
One deficiency of line projection methods results from the distribution of optical flux over the area occupied by the line image(s). In relatively compact systems where the illumination volume is small (laboratory or certain industrial applications), the luminous flux required to illuminate the object area is usually much less compared to submarine applications where the surveyed area is large. Because detection is reliant upon a minimum level of object illumination, i.e., flux per unit area, and because of optical absorption or scattering loss in the aqueous medium, submarine applications usually require a larger radiant flux from the source. In addition, remotely piloted or autonomous vehicles used in undersea operation prefer the use of highly efficient systems due to energy limitation inherent in their design. By reducing the area of the projected light patterns in accordance with this invention, it is possible to reduce the optical flux requirement from the source. Hence, the size and power consumption of the source is correspondingly reduced.
Additional concern stems from the need of submarine illumination systems to operate in an environment having uncontrolled lighting. For example, shallow-water submarine systems are subject to receiving background illumination from the sun. In such case, suppose that ambient lighting from the sun is present over a section of the benthonic surface yielding an illumination of R.sub.o watts over the image area and that this optical flux is distributed over the spectral region where the image detector is sensitive. In order to achieve detection of the projected pattern from the vision system, it is necessary that the projected radiance in each element of the pattern exceed that of the background by some factor, preferably greater than one. Thus, a projector uniformly distributing flux over the image area would require an output greater than R.sub.o assuming a lossless medium. Alternately, a projection of lines having equal light and dark width would require a flux greater than R.sub.o /2 since only half of the image area would be illuminated. The required source flux R.sub.s for arbitrarily shaped illumination will be R.sub.s =R.sub.o x (area of projection)/(image area), and if this shaped illumination is an array of small, spaced dots, much less light, e.g., 60% less, is required to provide acceptable determinations to be made.
Notwithstanding the extensive prior work and developments with structured illumination systems for ranging and remote profiling of objects, substantial improvements are still needed in such art, particularly for the submarine systems.